Cleaning up geometry after Boolean cuts
You could do it this way, and by the way you could have done it without booleans. Use the knife tool (K to activate, C to cut orthogonally, Z to cut through, E to continue, Enter to validate). To delete the bad edges, select them and X &gt; Dissolve Edges.

You could try to simplify, actually it all depends on what you're planning to do later, but as Gorgious says you'll need to keep some edges between your holes and the external edges: